Solution for anodic polishing of steel and iron articles



Patented Jan. 3, 1950 UNITED STATES PATENT OFFICE sow'rros roa ANODIC rorlrsnme or s'rmu. AND mos narrows Milton B. Hammond, Edgeworth, and Glade B. Bowman, Coraopolis, 2a., assignora to Standard Steel Spring Company, Coraopoiia, Pa., a corporation oi Pennayl No Drawing. Application March 8, 1947, Serial No. 733.426

This invention relates to a solution for use in the anodic electrolytic polishing of steel and iron articles. In such processes the steel or iron artia red deposit is formed on the steel article. We

have found that by including sulphate ion in proper amount in a solution in which phosphoric acid is the principal constituent, we can cause the precipitation of iron sulphate from solution so as to maintain the concentration of iron in solution below a certain critical value such that the solution operates satisfactorily in polishing the steel. We have found that the iron metal in solution should be maintained below one ounce per gallon for satisfactory results.

In accordance with our invention, we include in a bath which consists principally of phosphoric acid, sodium sulphate or other alkali metal or ammonium sulphate in such amount as to react with the iron in solution and precipitate it and maintain the concentration of iron metal in solution below one ounce per gallon. It is pre-;

ferred that the solution also contain a small amount of sulphuric acid, 1. e., up to 4% by weight of the solution, but the sulphuric acid can be omitted provided there is sumcient alkali metal or ammonium sulphate present to maintain the iron in solution below the critical value.

A preferred solution according to our invention is as follows, all percentages being by weight and in the case of the acids, we mean per cent by weight of 100% acid. course the acid employed need not be oi 100% strength but can be oi the strength comercially available.

7 Claims. (Cl. 204-1405) 2 The solution may contain the ingredients within ranges as follows:

Range Preierred Percent Percent Phosphoric 'Acid 55 to 86 60 to 70 Sulphuric Acid 0. 1 to 4 1 to 4 Water 7 to 30 15 to 30 'lri-sodium Phosphate. l to 15 1 to 6 Sodium Sulphate at least 0. 5

As mentioned previously, the sulphuric acid may be omitted entirely provided there is sufilcient sodium sulphate or its equivalent to maintain the'iron in solution below the critical value. The amount of sodium sulphate or its equivalent depends upon the amount of iron in solution. The solution will operate satisfactorily at the start of the process without any sodium sulphate or sulphuric acid, but after a time it is necessary to 'provide the sulphate ion required to cause precipitation of the iron thereby keeping the iron in solution below the critical value. In general, the sodium sulphate shouldamount to at least 0.5% and it is preferred that the sodium sulphate be present in such amount as to saturate the bath and leave an excess of undissolved sodium sulphate in the solution. This excess acts as a reservoir for supplying the sulphate ion required for maintaining the iron in solution below the critical value. There is no upper limit to the amount of sodium sulphate which the bath may contain since it is desirableto have an excess in solid form.

While sulphuric acid is not essential, provided there is sumcient sodium sulphate or its equivalent present, the preferred solution contains some sulphuric acid but not over 4%.

In place of sodium sulphate, we may employ other alkali metal or ammonium sulphates, for example, potassium sulphate, lithium sulphate and ammonium sulphate.

The tri-sodium phosphate reduces the chemical attack of the solution on the article before current is applied and increases the polishing action after current is applied. In general, the amount of tri-sodium phosphate should be increased as the percentage of water in the solution increases. In place of tri-sodium phosphate, we

may use other tri-alkali phosphates, di-alkali or other suitable flocculating agent. The preferred bath contains about 0.5% of gelatin but amounts of flocculating agent'within the range of 0.1% to% maybeused.

In using the solution in the anodic polishing of steel, it is preferred to carry out the process at an anode current density of about 285 amps.

per square foot and at a temperature of about 190 F. However, the solution may be used under widely varying conditions, the anode current density being as low as 25 or as high as 2000 amps. per square foot and the temperature can be any temperature up to about 250 F. The time it for polishing the steel will vary depending upon the polish required, from about 1 minute to 20 minutes, the usual period being about 5 minutes.

The invention is not limited to th preferred ingredients or proportions but may be otherwise embodied or practiced within the scope of the following claims.

We claim: I

1. A solution forruse in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 7 to 30% water, 1 to of a member of the class consisting of tri-alkali metal phosphate, di-alkali metal phosphate, mono-alkali metal phosphate, and phosphorus pentoxide, and at least 0.5% of a sulphate of the class consisting of alkali metal sulphate and ammonium sulphate.

2. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode; said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 0.1% to 4% sulphuric acid, '7 to 30% water, 1 to 15% of a member of the class consisting oftri-alkali metal phosphate, di-alkali metal phosphate, mono-alkali metal phosphate,

and phosphorus pentoxide, and at least 0.5% of a sulphate of the classconsisting of alkali metal sulphate and ammonium sulphate.

3. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 1% to 4% sulphuric acid, '7 to 30% water, 1 to 15% tri-sodium phosphate, and at least'0.5 of alkali metal sulphate.

4. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to phosphoric acid, 0.1% to 4% sulphuric acid, '1 to" 30% water, 1 to 15% tri-sodium phosphate and at least 0.5 alkali metal sulphate.

5. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 7 to 30% water, 1 to 15% of a member of the class consisting of tri-alkali metal phosphate, di+alkali metal phosphate, mono-alkali metal phosphate, and phosphorus pentoxide, and a sulphate of the class consisting of alkali metal sulphate and ammonium sulphate, said sulphate being present in amount sumcient to at least saturate the solution.

.6. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 0.1% to 4% sulphuric acid, 7 to 30% water, 1m 15% tri-sodium phosphate and alkali-metal sulphate in amount sufllcient to at least saturate the solution.

7. A solution for use in the electrolytic polishing of steel and iron articles wherein the article is employed as an anode, said solution consisting essentially of and containing by weight 55 to 85% phosphoric acid, 0.1% to 4% sulphuric acid, '7 to 30% water, 1 to'l5% of a member of the class consisting of tri-alkali metal phosphate, di-alkali metal phosphate, mono-alkali metal phosphate and phosphorus pentoxide, 0.1% to 5% of a flocculating agent for 'iron sulphate, and at least 0.5% of a sulphate of the class consisting of alkali metal sulphate and ammonium sulphate.

' NHLTON B. HAMMOND.

GLADE B. BOWMAN.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Proceedings of The American Electroplaters Society, 1941, pages 109, 110. 

1. A SOLUTION FOR USE IN THE ELECTROLYTIC POLISHING OF STEEL AND IRON ARTICLES WHEREIN THE ARTICLE IS EMPLOYED AS AN ANODE, SAID SOLUTION CONSISTING ESSENTIALLY OF AND CONTAINING BY WEIGHT 55 TO 85% PHOSPHORIC ACID, 7 TO 30% WATER, 1 TO 15% OF A MEMBER OF THE CLASS CONSISTING OF TRI-ALKALI METAL PHOSPHATE, DI-ALKALI METAL PHOSPHATE, MONO-ALKALI METAL PHOSPHATE, AND PHOSPHORUS PENTOXIDE, AND AT LEAST 0.5% OF A SULPHATE OF THE CLASS CONSISTING OF ALKALI METAL SULPHATE AND AMMONIUM SULPHATE. 